In long-haul optical transmission systems, signals are typically transmitted at data rates on the order of 10–40 Gb/s. The bits in these signals degrade as the signal travels over the optical fiber. The shape of the bits are attenuated due to fiber loss or fiber dispersion and the timing of bits drifts due to jitter. Before the bits degrade to an unrecoverable point, they must be corrected or regenerated for further transmission.
When a digital optical signal has degraded sufficiently, then 3R regeneration—reamplification, retiming, and reshaping—of the optical pulses is required. In existing systems, optical amplification is provided by erbium-doped fiber amplifiers (EDFA). EDFAs are optical repeater devices that are used to boost the intensity of optical signals being carried through a fiber optic communications system. However, EDFA's are unable to retime or reshape the pulses. Instead, retiming and reshaping of the optical data bits must be performed electronically.
The use of electronics leads to a significant bottleneck in the scalability of the network as well as an exorbitant cost per bit due to the processing required to reshape and retime bits at high data rates. Moreover, each wavelength in the optical signal must be divided out into separate channels and processed by separate electronic circuits. To avoid the cost and complexity of optical-electronic conversion, it would be advantageous to carry out 3R regeneration entirely in the optical domain, thereby eliminating the electronic regeneration bottleneck. However, prior systems do not perform optical reshaping or retiming of data signals.